DiscussionRoman numerals are written using the letters M, D, C, L, X, V,and I, representing the values 1000, 500, 100, 50, 10, 5, and 1,respectively. The first regex matches any string composed of theseletters, without checking whether the letters appear in the order orquantity necessary to form a proper Roman numeral.In modern times (meaning during the past few hundred years),Roman numerals have generally been written following a strict set ofrules. These rules yield exactly one Roman numeral per number. Forexample, 4 is always written as IV, never as IIII. The second regex in the solution matchesonly Roman numerals that follow these modern rules.Each nonzero digit of the decimal number is written out separately in the Roman.Get Regular Expressions Cookbook now with O’Reilly online learning.O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.
noun
General rule is if a literal with bigger value comes before a literals with smaller value or same value, the resulting number is their sum, for example XIII means 10+3=13 or XX = 10. And also if a literal with smaller value comes before a literals with bigger value, the resulting number is their subtraction, for example IV means 5–1=4.
one of the numerals in the ancient Roman system of notation, still used for certain limited purposes, as in some pagination, dates on buildings, etc. The common basic symbols are I (=1), V (=5), X (=10), L (=50), C (=100), D (=500), and M (=1000). The Roman numerals for one to nine are: I, II, III, IV, V, VI, VII, VIII, IX. A bar over a letter multiplies it by 1000; thus, X̅ equals 10,000. Integers are written according to these two rules: If a letter is immediately followed by one of equal or lesser value, the two values are added; thus, XX equals 20, XV equals 15, VI equals 6. If a letter is immediately followed by one of greater value, the first is subtracted from the second; thus, IV equals 4, XL equals 40, CM equals 900. Examples: XLVII(=47), CXVI(=116), MCXX(=1120), MCMXIV(=1914). Roman numerals may be written in lowercase letters, though they appear more commonly in capitals.
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Origin of Roman numeral
Dictionary.com UnabridgedBased on the Random House Unabridged Dictionary, © Random House, Inc. 2020
British Dictionary definitions forroman numerals
pl n
the letters used by the Romans for the representation of cardinal numbers, still used occasionally today. The integers are represented by the following letters: I (= 1), V (= 5), X (= 10), L (= 50), C (= 100), D (= 500), and M (= 1000). If a numeral is followed by another numeral of lower denomination, the two are added together; if it is preceded by one of lower denomination, the smaller numeral is subtracted from the greater. Thus VI = 6 (V + I), but IV = 4 (V – I). Other examples are XC (= 90), CL (= 150), XXV (= 25), XLIV (= 44). Multiples of a thousand are indicated by a superior bar: thus, ̅V = 5000, ̅X = 10 000, ̅X̅D = 490 000, etc
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Cultural definitions forroman numerals
Letters of the alphabet used in ancient Rome to represent numbers: I = 1; V = 5; X = 10; L = 50; C = 100; D = 500; M = 1000. The numbers one through ten are written I, II, III, IV, V, VI, VII, VIII, IX, and X. Roman numerals are often used to signify divisions of a long work, or of a work with many parts. They are also used to lend significance to something, as in Super Bowl VII. Formal designation of years may also be in Roman numerals: a.d. MCMLXXXIX = a.d. 1989.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.